Nuclear reactor cooling water

Patent Pending PROBLEM TO BE SOLVED: To provide a method and a device for selecting a hydrogen peroxide concentration as a corrosive environment index, and determining directly the hydrogen peroxide concentration in high-temperature water. ; SOLUTION: A probe supporting a pair of electrodes and a reference electrode by an insulating material is arranged in cooling water in a reactor or in a pipe communicated with the reactor, and either of the pair of electrodes is kept at a natural potential to the reference electrode, and an alternating voltage is applied to the other electrode, and a frequency is changed and a complex impedance between the pair of electrodes is measured.